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  #1  
Old 09-08-2007, 02:40 PM
chetwesley's Avatar
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300SD Brake Pads

My brake wear light is coming on pretty often when I am stopped at a stop light, so I am thinking it may be time to replace the pads.

I know there must be at least 100 people here who have done this job... so, can one of you give me the basics? I hear it is easy, just would like some info to read first.

I have done only one pad replacement before, which was on a 2002 chevy prism, and which was aok no problems.

I've done a search on the forum and haven't found a step-by-step on replacing the pads. Can anyone point me to a thread or a link on the web appropriate to this type of breaks... even if it is a general guide which is suited to these types of brakes.

I understand they are four wheel disk breaks, which I think is different than the job I have done previous. Should I assume I will be replacing all four sets of pads?

Thanks for any help.
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  #2  
Old 09-08-2007, 02:54 PM
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This is real basic but it might help.


These are two piston calipers. Remove only one pad and replace at a time.
1) Jack up car
2) Remove wheel
3) Disconnect sensor wires
4) Un bolt sensor plug
5) Remove spring clips from pin ends
6) Drive out pins
7) Remove two retainer springs
8) Use channel locks to squeeze pad and piston back into caliper
9) Pull out pad
10) At this point you may need to squeeze the piston in farther
11) Install new pad
12) Repeat on inboard pad
13) Replace two retainer springs
14) Replace pins
15) Replace spring clips
16) Re bolt sensor plug
17) Re connect sensor wires
18) Put wheel back on
19) Lower car
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  #3  
Old 09-08-2007, 03:14 PM
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Thanks, a lot, that is exactly what I needed... not much different actually from the chevy prism, minus the sensors and I think plus an extra piston... It looks from your description like there are pistons that push on both the inner and outer pads? Is that right, is that what you mean by there are two piston calipers?

A couple questions for whoever knows:

- Should I open the cap on the break fluid reservoir? Probably, right?

- Should I plan on doing all four, or is it commonly just the front ones that wear down first?

- Do you have to suspend the caliper in any way to support it while you take out the pads? When I helped my dad with this job on my old minivan, we had to hang the caliper by a wire to keep stress off of the hoses (so the caliper wasn't hanging by the hoses when they were removed). I can't remember if I had to do that on the prism, or if you could just keep a bolt in and pivot the caliper up or something.

Any other tips or additions would be much appreciated.
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Sold but fondly remembered: 1981 300TD Turbo Tan 235K miles, 1983 300SD Astral Silver 224K miles

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  #4  
Old 09-08-2007, 03:22 PM
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You don't have to remove the calipers to get the pads off- just use a set of channel locks to squeeze the old pads away from the rotor and they will just slide out (after removing the pins, of course).

When was the last time you did a brake job? If you don't know, I would replace all four. It is really up to you, though, and how much you want to put at risk.
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  #5  
Old 09-08-2007, 03:23 PM
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And taking the cap off the reservoir will make the job easier.
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  #6  
Old 09-08-2007, 05:23 PM
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Drape a clean rag over the open reservoir. Brake fluid back-splash, when compressing the wheel cylinders, makes a mess of a good paint job.
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  #7  
Old 09-08-2007, 05:29 PM
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Take a look at the thickness of the rear pads, but they usually last at least 3x as long as the front ones do...probably don't have to replace them.

Make sure the front rotors are still to spec...if they have really deep ridges on them or a huge lip on the edge of the rotor they may need to be replaced as well, which is a much bigger job.
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'01 E320 Wagon - 159k - mine (OC-160,000)
'01 E320 - 179k - dad's (OC-182,500)
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  #8  
Old 09-08-2007, 06:23 PM
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You might want to measure the rotor thickness as mentioned, fronts 10.6mm or .418 inch. Rears, 8.3mm or .327 inch. Service limit on pads are 1.5mm all around. You will need to replace rotors if they are below spec, when they get too low, the caliper piston will push completely out, causing a no brake condition. Not good.
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  #9  
Old 09-08-2007, 07:38 PM
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Replacing the rotors once the pads are out is not all that much more work. All you need to do at that point is remove the two caliper bolts, suspend the caliper, remove the hex set screw and pull the rotor off. It's an extra 15 min per wheel at most.

I use a big flat head screw driver to push the pad all the way back before removing. Never scratched or bent a rotor yet. I am usually pretty careful when doing it though.

I use a center punch to drive out the pins BTW.
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  #10  
Old 09-08-2007, 08:34 PM
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If the light on the dash is comming on that only means the front pads are worn. You have to look at the rears to decide.
To add to what I put up earler ( and others have already mentioned most)
Remove the reservoir cap and drape something over it so nothing falls in. I usually just rest the cap on top.
The calipers can stay on but do one pad at a time because there is a piston on each side and it makes it easier to push in that piston if the other pad is in place.
I used channel locks to squeeze in the old pad/piston before removing the pad.
Replace the sensors whenever you change the brakes. Sensors are cheap.
I have used a drift pin, a nail and a small phillips head screw driver to push out the pin, what ever works.
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  #11  
Old 09-08-2007, 09:33 PM
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Quote:
Originally Posted by davidmash View Post
Replacing the rotors once the pads are out is not all that much more work. All you need to do at that point is remove the two caliper bolts, suspend the caliper, remove the hex set screw and pull the rotor off. It's an extra 15 min per wheel at most.

I use a big flat head screw driver to push the pad all the way back before removing. Never scratched or bent a rotor yet. I am usually pretty careful when doing it though.

I use a center punch to drive out the pins BTW.

Not on a W126 300sd its not....you need to remove the hub, then remove the rotor from the hub, replace the wheel bearing seals, and re-pack the bearings with grease, then re-assemble properly with the right tightness on the locknut on the spindle. Not as easy as on the later cars. And a lot of the time the hub can be a pain to get off the rotor as it has allen bolts which are often stuck.
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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 83k - mine - (OC-85,500)
'17 Metris(VITO!) - 13k - wifes (OC-17k)
'01 E320 Wagon - 159k - mine (OC-160,000)
'01 E320 - 179k - dad's (OC-182,500)
'07 E350 Wagon - 131k - dad's (OC-132,500)
'01 SL500 - 51k - dad's (OC-52,000)
'16 E400 4matic Sedan - 57k - Brothers (OC-64,000)
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  #12  
Old 09-09-2007, 12:00 PM
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Quote:
Originally Posted by davidmash View Post
Replacing the rotors once the pads are out is not all that much more work. All you need to do at that point is remove the two caliper bolts, suspend the caliper, remove the hex set screw and pull the rotor off. It's an extra 15 min per wheel at most.
You must be referring to the rear brakes only. If you can replace the front rotors on a W126 in 15 minutes, I would like to come to Dallas and take a lesson from you!!!
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  #13  
Old 09-09-2007, 12:38 PM
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Wow, I did not know the 126 was different from the rest of the cars of that time. My car and the E300 (as far as I can tell by looking) replace as mentioned above.

Why the change on the 126?

AS I Said above, I have not changed the 300e yet (but in about 2 or 3k I will need to) am I in for any surprises?
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  #14  
Old 09-09-2007, 12:53 PM
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Quote:
Originally Posted by davidmash View Post
Wow, I did not know the 126 was different from the rest of the cars of that time.
It's not.
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  #15  
Old 09-09-2007, 01:20 PM
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add anti squeel paste to the back of the pads as well
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